7th Ponty Fly In - Mystery Model

[Shaun]

It's almost finished Al just a few bits of wood to go... don't worry about making mods and changes to the original design, it all adds to the fun.

Anybody up for a Tri-plane or twin motor version

Shaun

[stuart mackay]

Short kit arrived today, thanks Neil!
It joins the ever growing list of "Roundtoits"

[Shaun]

Stuart, if you're going to East Kirby you can build it while dinner cooks one evening.

Shaun

[PaulJ]

Without giving too much away, the variant I have in mind may need a little extra power and I happen to have a 2205 1850kv motor, rated at 80 watts in my spares box. It is possibly a bit OTT and the limiting factor could be the size of prop you can use on this model......... What are the implications of using a prop that is too small for a given motor?

[Martin]

For battery-powered models, if the prop's too small then you get less thrust - no harm done if you have enough thrust to fly, and the current drawn from the battery is correspondingly less, so you get potentially longer flight times. Some people believe that the motor might over-speed, but that doesn't happen - even on no load the motor won't spin faster than the battery voltage multiplied by the motor KV.

If you don't have enough thrust to fly, then you have three options without increasing the propeller diameter:

• More pitch on the prop (but this doesn't usually give much more static thrust - mainly it just gives a higher flying speed (if the model is capable of that). Also usually once the pitch exceeds the diameter you get problems with the blades stalling.
• More blades on the prop - you can buy small props in three and four blade format (they're used on multirotors). You could try stacked props if the motor shaft/prop drive is long enough to take them, but you don't get double the thrust by using two props as the back propeller is acting in the prop wash of the front one. Contra-rotating props are the answer to this, but not really practical (?) for the Pulstar.
• More RPM: this either needs a motor with a higher KV, or you need more cells if you're using the same motor. Check that the motor and speed controller are rated to handle the number of cells you're switching to. Check that the propeller is rated to handle the increased rpm. The theoretical rpm is the battery voltage multiplied by the KV of the motor, so with a 3-cell battery (nominally 11.1V) and a 2000 KV motor, that would result in about 11.1 x 2000 = 22,200 rpm.

A small ducted fan unit might be worth a try. There is (was?) a HobbyKing foamy glider that has a small ducted fan mounted above the wing, and it sounds lovely - not the usual EDF whine - more of a turbine-like 'whoosh'.

[PaulJ]

Martin, many thanks for this........ As long as it wouldn't overheat or burn anything out, I guess it's worth a try perhaps with a 4 bladed prop. I see HK do some 4" dia, 4" pitch 4 bladers that might be worth trying....... Thanks again.

Paul

[Shaun]

Hi Paul,
As Martin said you can't over rev an electric motor when using the specified voltage range, only damage them with too much current draw by using an over sized prop and loading it up. The prop you mention will work fine on the motor but make sure you use a CCW one as they tend to come in pairs CW & CCW for multirotors.

If you are building it as per plan it only needs around 25 - 30 watts as it's basically a powered glider (mine weighed under 8 ozs including the LiPo). That motor you are considering will give out some significant go juice

Shaun

[GeeW]

My iGull kit hoved into view today, so thank you to Neil. Will be digging motor, ESC and servo out this very evening to see how it might all fit (or not)!

Gordon

[Igull]

Talking of Pulstar kits, there's one wee thing on the fuselage sides, they're marked L & R on the rear section for a reason (other than the obvious ) When cutting jigsaw or any other style joint where it needs to have an accurate fit, the laser beam is always at a slight angle to the vertical, so , you need to cut from what is essentially the opposite side to get an exact matching part (as well as ensuring a beam offset too - it's only 0.08mm, but it does matter - to me at least ). So, the side marked L goes with the left fuselage side and vice versa.
It's a small thing, but it makes the joint less visible.
One final thing, any slight 'smokiness' caused by the laser on the rear can be wiped off with a dampish handkerchief - easier than trying to sand it off
Cheers
Neil

[Martin]

My Pulstar kit arrived Thursday. Thanks Neil!

I'm looking at lashing up some sort of pulse motor to control the rudder. I've programmed an Arduino to drive a H-bridge. It decodes 3 radio channels to give:

• Left/right ratio for steering.
• Pulse rate (elevator) - not required for the Pulstar but interesting to try different pulse rates to see how it affects steering and battery drain - and I might try elevator in the future either on the Pulstar or a different model.
• Auxiliary channel to control the amount of power delivered to the pulse motor - the idea is that the motor doesn't have to be driven always left or right - it can also 'coast' for parts of each pulse cycle to save battery power - a rotary knob or slider on the transmitter allows the percentage of time the motor is actually powered to vary from 0% to 100%.

I have some of these small motor/metal gearbox units from Ebay at a couple of quid each.


https://www.ebay.co.uk/itm/1pc-DC-6V-30 ... SwoJZXSQjQ

The standard gearbox gives much too great a reduction for pulse-steering applications (though the final output is very high torque and I can think of other uses for one). It looks like I can remove the gears from the 'second layer' and use just the reduction gears of the first layer to drive the output arm / spring return lever for the pulser. The motor is rated 6V continuous and seems quite happy even at 8V so I might be able to drive it direct from the 2-cell flight power pack.

It may all come to nothing if I hit a snag or get enticed away by some other project, but at the moment it looks quite promising.